This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The quantitative comparison of glycan expression requires highly sensitive methods that can distinguish and identify individual glycans with subtly different structures. Mass spectrometry (MS) fulfills these requirements while providing a rapid and reliable method to analyze complex mixtures, and therefore has been widely used in glycomic studies. One limitation of using MS for the quantitation of biomolecules is that the ionization efficiencies of distinct molecular species can differ significantly, depending on such factors as the analyte's molecular mass, proton/cation affinity, surface activity, the presence of compounds which compete with or interfere with the ionization of the analyte, etc. We are involved in devising new methodologies to improve the accuracy of comparative glycomic experiments.